In transmitting DC electric energy, for example, in DC transmission, the power factor is always 1 because the DC electric energy has no frequency. There is no power loss attributable to a skin effect or corona loss. Furthermore, a required insulation level can be reduced. Since it is unnecessary to consider the reactance and phase angle of a power line, the stability is comparatively high and the power transmission capacity is not limited. In addition, short-circuit current is low, thus making connection of different frequency AC systems possible. Furthermore, there is little inductive interference.
Due to the above-mentioned reasons, high-voltage DC transmission is recently used; however, 100% of produced DC electric energy cannot be transmitted to a desired place because of problems with mechanism in transmitting power.
A power transmission system is required to transmit produced power to a desired place. The power transmission system uses a power line through which produced power is transmitted.
In such a power transmission system using a power line, 100% of produced power cannot be used in a desired place by because a power loss occurs on the power line.
At present, only about 80% of produced power can be used because of a power loss and reverse current that occur during transmission of power through the power line.
To make a high-efficiency power transmission system at low cost, it is necessary to reduce a power loss from the power line as much as possible.